Cannot override apply function - kotlin

Question

I came across the following code:
import io.reactivex.Observable
import io.reactivex.functions.BiFunction
import java.util.concurrent.TimeUnit
class ExpBackoff(
private val jitter: Jitter,
private val delay: Long,
private val unit: TimeUnit,
private val retries: Int = 0
) : Function<Observable<out Throwable>, Observable<Long>> {
#Throws(Exception::class)
override fun apply(observable: Observable<out Throwable>): Observable<Long> {
return observable
.zipWith(Observable.range(1, retries), BiFunction<Throwable, Int, Int> { _, retryCount ->
retryCount
})
.flatMap { attemptNumber -> Observable.timer(getNewInterval(attemptNumber), unit) }
}
private fun getNewInterval(retryCount: Int): Long {
var newInterval = (delay * Math.pow(retryCount.toDouble(), 2.0) * jitter.get()).toLong()
if (newInterval < 0) {
newInterval = Long.MAX_VALUE
}
return newInterval
}
}
located at:
https://leandrofavarin.com/exponential-backoff-rxjava-operator-with-jitter
This code doesn't compile. This line is wrong:
Function<Observable<out Throwable>, Observable<Long>>
Function only takes a single argument. I am really confused here. The person who wrote the article clearly indicates that he wrote this code and I assume it works or at least worked at the time he wrote it. But I doubt that Kotlin changed the interface for Function. Even if I remove the second parameter, the code will not compile because the apply function cannot be overridden as this is not part of the Function interface.
How can I fix this issue?

Answer 1

Looks like you are missing correct Function import. The following code works in my IDE.
import io.reactivex.Observable
import io.reactivex.functions.BiFunction
import io.reactivex.functions.Function
import java.util.concurrent.TimeUnit
class ExpBackoff(
private val jitter: Jitter,
private val delay: Long,
private val unit: TimeUnit,
private val retries: Int = 0
) : Function<Observable<out Throwable>, Observable<Long>> {
#Throws(Exception::class)
override fun apply(observable: Observable<out Throwable>): Observable<Long> {
return observable
.zipWith(Observable.range(1, retries), BiFunction<Throwable, Int, Int> { _, retryCount ->
retryCount
})
.flatMap { attemptNumber -> Observable.timer(getNewInterval(attemptNumber), unit) }
}
private fun getNewInterval(retryCount: Int): Long {
var newInterval = (delay * Math.pow(retryCount.toDouble(), 2.0) * jitter.get()).toLong()
if (newInterval < 0) {
newInterval = Long.MAX_VALUE
}
return newInterval
}
}